The propose studies will define further the mechanisms of host resistance to leprosy and will evaluate the potential efficacy of immunotherapeutic measures for leprosy which involve the use of the synthetic adjuvant muramyl dipeptide and its analogs and killed suspensions of Corynebacterium parvum. In addition the proposed studies will evaluate the functional capabilities of mononuclear phagocytes from the peripheral blood of patients with untreated lepromatous leprosy.